The present invention relates to an image pickup apparatus with high resolution capability, particularly with image storage function.
A video signal obtained by picking up an optical image of an object with an image pickup apparatus can be easily processed such as editing, image trimming and the like. Recording/reproducing a video signal can also be easily performed by using an erasable/rewritable memory. With a conventional image pickup apparatus, an optical image of an object is focussed onto a photoconductive region of an image pickup element by a taking lens then converted into electric image information. The electric image information is time sequentially outputted as a video signal. Various image tubes or solid state image pickup elements have been used for such conventional image pickup apparatus.
It is also known that various new television systems such as EDTV, (Extended definition TV) HDTV (High definition TV), and the like have been proposed for recent requirements of high quality and resolution of reproduced images.
In order to reproduce images with high quality and resolution, it is necessary for an image pickup apparatus to generate a video signal from which an image of high quality and resolution can be reproduced. However, an image pickup apparatus using an image tube has a limit in reducing the diameter of an electron beam, and also the target capacitance thereof increases as the target area made large, resulting in a poor resolution. Further, for high resolution moving images, the necessary frequency band for such a video signal would become larger than several tens to hundreds MHz, thus posing a problem of poor S/N. The above problems have made it difficult to obtain reproduced images of high quality and resolution.
More specifically, in order to obtain a video signal from which an image of high quality and resolution can be reproduced, it is necessary to reduce the diameter of an electron beam or make a large target area without causing a capacitance increase. However, there is a limit in reducing the diameter of an electron beam because of the capability of electron gun and the structure of focussing system. If the target area is made large using a large taking lens, the target capacitance becomes inherently large so that the high frequency components of a video signal is degraded and hence the S/N thereof becomes considerably poor. Thus, it is impossible for an image pickup apparatus with an image tube to obtain a video signal for a reproduced image of high quality and resolution.
In the case of an image pickup apparatus with a solid state image pickup element, in order to obtain a video signal from which an image of high quality and resolution can be reproduced, it is necessary to use a solid state image pickup element having a large number of picture elements pixels. However, with the solid state image element having a large number of picture elements, the drive clock frequency becomes high (in the case of moving images, it would be about several hundreds MHz) and the capacitance of the drive circuit becomes large as the number of picture elements increases. The clock frequency currently used for a solid state image pickup element is generally about 20 MHz so that such an image pickup apparatus cannot be realized in practice.
As described above, conventional image pickup apparatus cannot generate a video signal suitable for high resolution and quality of reproduced images.
In the meantime, the image pickup element of a conventional image pickup apparatus has not a long term memory function by itself to store object images, but it merely obtains an electric video signal through photoelectric conversion of optical information in response thereto. Thus, if it is required to store picked-up electric information signals, an additional magnetic storage for example becomes necessary. It has been long desired accordingly to provide an image pickup element having by itself a memory function.